In general, a wireless communication system provides a wireless communication service and includes Base Stations (BSs) and user terminals (or Mobile Stations (MSs)). The BS and the MS performs wireless communication by using transmission frames. Thus, the BS and the MS must acquire mutual synchronization and must search a cell ID for transmission/reception of the transmission frames. For the synchronization acquisition and the cell ID search, the BS transmits a synchronization signal so that the MS can detect the start of a frame transmitted from the BS. To this end, the BS performs an Inverse Fast Fourier Transform (IFFT) operation on a frequency-domain binary preamble sequence to transform it into a time-domain complex preamble sequence, and transmits the time-domain complex preamble sequence to the MS. The MS receives a synchronization signal of a complex preamble sequence from the BS to detect the frame timing of the BS, and demodulates a received frame according to the detected frame timing. In general, the synchronization signal uses a specific preamble sequence predefined between the BS and the MS.
An OFDM system allocates an OFDM symbol for synchronization acquisition and cell ID search. Using the OFDM symbol, the synchronization acquisition and the cell ID search may be performed by the following two methods.
In the first method, a BS allocates a sequence only to the even-numbered subcarrier in a frequency domain, performs an IFFT operation, generates a repetition structure in a time domain, and transmits the same to an MS. The MS acquires synchronization by using the time-domain repetition structure, acquires a frequency-domain sequence through a Fast Fourier Transform (FFT) operation, and searches a cell ID by using the frequency-domain sequence. The first method is low in complexity because it acquires synchronization by using the repetition structure. However, the first method is poor in performance because it uses a small length of sequence for synchronization acquisition.
In the second method, without using the repetition structure, a BS allocates sequences to all subcarriers in a frequency domain, wherein a synchronization acquisition sequence and a cell ID search sequence are allocated to subcarriers in a division manner. The second method may perform cell ID search and synchronization acquisition through various decoding schemes. One of the decoding schemes extracts a synchronization acquisition sequence by means of a band-pass filter, acquires synchronization in a time domain by means of the synchronization acquisition sequence, acquires a cell ID search sequence through an FFT operation, and searches a cell ID in a frequency domain by means of the cell ID search sequence. Another of the decoding schemes performs an FFT operation on a received sequence at each time to acquire synchronization in a frequency domain and search a cell ID in a frequency domain. The second method is good in performance but is high in complexity.
What is therefore required is a new sequence allocation method for synchronization acquisition and cell ID search in a wireless communication system, which can overcome the limitations of the first method and the second method.